The present invention relates to a recording/playback device in a camera system employing electrophotography and a recording medium for use in such a system.
Referring to the accompanying drawings, a description will first be given of a recording medium composed of conventional semiconductor elements together with a recording/playback device therefore. In FIG. 1, there is shown a discoid recording medium 1 having a surface covered with a laminated recording material for the purpose of recording/playback. The recording medium 1 is turned by a driving gear 2 in a predetermined direction Y at a constant speed, whereas a stylus 3 is moved in the radial direction X of the recording medium 1 at a constant speed to scan the surface of the recording medium 1; i.e., the recording medium 1 is linearly spirally or concentrically scanned as the stylus 3 moves in the radial direction X.
The stylus 3 is connected via a coil 4 to an input/output circuit 5 and, when an input signal is recorded, the signal is supplied via the coil 4 to the stylus 3 while scanning is effected. When the signal is read out (played back), on the other hand, the stylus 3 is used to detect changes of electrostatic capacity as scanning is conducted, and the signal thus detected is supplied via the coil 4 to the input/output circuit 5.
Referring to FIG. 2, the structure of the recording medium 1 and the principle of recording/playback will subsequently be described. FIG. 2 is a sectional view of the recording medium taken on a line Z--Z in FIG. 1. As shown in FIG. 2, a silicon dioxide film (SiO.sub.2) layer 7 and a nitride film (Si.sub.3 N.sub.4) 8 are laminated on the surface of a semiconductor substrate 6 of n-type monocrystalline silicon, whereas a conductive layer 9 is formed by aluminum evaporation on the undersurface thereof.
At the time of recording/playback, the conductive layer 9 is set at ground potential and the stylus 3 is moved to scan the surface of the nitride film 8. When an input signal is recorded, a voltage corresponding to the voltage level of the input signal is applied via the stylus 3 to the nitride film 8 and, as resulting charges 10a are produced in the nitride film 8, a depletion layer 10b whose depth corresponds to the quantity of charge simultaneously appears within the semiconductor substrate 9. Since the charges are accumulated and held in the nitride film 8 even though the recording medium 1 is removed from the system, the recorded data can be maintained therein over a long period of time. At the time of playback, the portion (track) on which the data has been recorded is scanned by the stylus 3 to detect changes of electrostatic capacity according to the presence or absence or the depth of depletion layer 10b so that the recorded signal is played back by means of the signal thus detected.
In the aforementioned prior art, however, the stylus and the nitrided film of the recording medium must be spaced as close as several tens of angstroms to effect recording/playback. When scanning is conducted with such a minute space therebetween, the stylus and the recording medium in practice unavoidably sometimes make contact with each other, causing wear of both members.
Moreover, since such a conventional arrangement is designed to record electric signals using the stylus on a track basis, i.e., to record/play back the electric signal which changes with time, it is therefore impossible to implement recording/playback in the same manner as in conventional photography wherein optical images are directly simultaneously two-dimensionally photographed using silver salt films. Although a solid-state pickup device such as a CCD has recently been developed to make it relatively easy to record optical images two-dimensionally, there still exists difficulty in simplifying the device in construction because the conversion data into time series signals is relied upon to effect recording/playback.